Process for producing alcohol and other bioproducts from biomass extracts in a kraft pulp mill

ABSTRACT

A method for the production of alcohol and other bioproducts from power boiler woody biomass extract containing hemicelluloses, with or without combining extract from wood prior to Kraft cooking. The process is integrated with the host Kraft pulp mill plant process to minimize the heat loss from extracting hemicelluloses and the energy used in the process.

FIELD OF THE INVENTION

This invention relates, in general, to the process extracting andtreating of extracts of biomass prior to a biomass boiler, potentiallycombined with extract from biomass prior to Kraft process, and treatmentof this extract for production of alcohol and other bioproducts in aKraft pulp mill.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be obtainedby reference to the following detailed description when read inconjunction with the accompanying drawings wherein:

FIG. 1. illustrates a conceptual flow sheet example of the inventionprocess.

FIG. 2. illustrates a typical general arrangement of the unit operationsfor mixed biomass derived extract by steam explosion prior to a powerplant combustor.

BACKGROUND OF THE INVENTION

Renewable power generation from forest residues is commonly practiced inthe forest products industries. The U.S. forest products industryconsumed 27.1 million tons of wood derived biomass, called “hog fuel”,in the generation of steam. By comparison, the power generation industryused 11.9 million tons of biomass of which 80% is wood derived. Thebiomass consumption in power generation is expected to double in every10 years until 2030.

The major wood components are lignin, hemicelluloses and cellulose. Thesteam explosion process dissolves predominantly hemicelluloses intemperatures above 160° C. Hemicelluloses fraction removed in thisprocess is termed “extract”. A concentration of the extract throughevaporation is energy intensive, although it is currently practiced toproduce molasses.

Previous research indicates that ethanol, acetic acid and theirbyproducts can be derived from the wood extract. Especially hardwoodproduces an extract rich in acetic acid and sugars as taught by Amidonet al. in (U.S. Patent Application No. 2007/0079944 A1, Apr. 12, 2007).

The current inventors, Retsina; et al. (U.S. Patent Filing No.61/175,588) have previously described a steam extraction and hydrolysisprocess, in which an alkaline acetate product is concentrated in reverseosmosis membrane from evaporator condensate. The clean permeate isfurther recycled to the host mill to achieve zero effluent operation.Furthermore, the current inventors Retsina; et al. (U.S. PatentApplication No. 61/219,764) have described the process integration ofthe waste heat to temper power boiler feed water.

The current inventors found an alternative method to produce fermentedalcohol, ethanol or butanol, from biomass extraction using steamexplosion, followed by vapor recompression evaporation, acid hydrolysis,fermentation and distillation. The present inventors have now developeda process, wherein the hemicelluloses in the power plant biomass extractcan be converted to chemical products in an energy efficient process.

SUMMARY OF THE INVENTION

The present invention describes a process for the production of alcoholand other bioproducts from power boiler biomass extract, combined ornot, with extract from the pretreatment of wood chips prior to Kraftprocess digestion. Treatment of hemicelluloses in the extract throughhydrolysis, evaporation, fermentation and distillation steps is used torecover and concentrate alcohol and acetate products. The process isintegrated with the host plant to reuse water and to minimize processenergy and water consumption.

DETAILED DESCRIPTION OF THE INVENTION

The first step of the process is biomass extraction. Woody biomass ischarged in a batch or continuous reactor vessel along with steam andheated to between 5 and 30 atmospheres pressure for 2 or more minutes toobtain 10-30% of wood as dissolved solids. In one manifestation, thisextract is combined with extract from the Kraft mill digester. In theKraft mill digester, a first stage of steam extraction is practicedprior to the Kraft cooking.

The second step of the process is washing of biomass. The heated biomassis washed with hot water or condensate and drained to recover dissolvedwood components. The wash filtrate contains dissolved xylan, glucan,mannan, arbinan, galactan and acetyl groups in oligomers ofhemicelluloses as well as lignin. The wash filtrate has low organicsolids concentration in between 1% and 15%. The majority of the watermust be removed before an economic treatment of hemicelluloses ispossible.

The third step of the process is compaction of the biomass. Theremaining solid biomass is subjected to mechanical pressure through aplug screw feeder. This compaction dewaters the biomass to uniformmoisture of 60% or less, which is similar to delivered biomass from theforest.

The fourth step of the process is low solids evaporation. Evaporation ofthe wash filtrate or extract using mechanical vapor recompression issuitable for low solids concentration up to around 25%, because theboiling point rise is small. Evaporated vapor is compressed andcondensed in the hot side of the evaporator to produce more evaporation.If the wash filtrate or extract feed concentration is over 5%, this stepmay be omitted. When the pH is kept below acetic acid dissociation pointat 4.8, acetic acid, a fermentation inhibitor, is volatilized to vaporfraction.

The fifth step of the process is hydrolysis. Sulfuric acid or enzymescan be used to hydrolyze the sugars, which were concentrated in the lowsolids evaporator. Oligomeric hemicelluloses are converted into monomersugars and acetyl groups are released. The hydrolyzate pH is controlledfollowing the hydrolysis to maintain acetic acid in the unassociatedform. Hydrolysis can be performed in batch or continuous mode. As anoption at the end of this step, the pH may be adjusted with lime oranother chemical and any precipitated solids may be washed and treatedseparately.

The sixth step of the process is post hydrolysis evaporation.Evaporation using mechanical vapor recompression is performed toconcentrate the hydrolyzate to 15%-35% solids. More of the remainingacetic acid and water is evaporated in this step. Under the appropriateeconomic criteria, this step could be done with steam evaporation.

The seventh step of the process is fermentation of wood sugars. Thesugars in the evaporated hydrolyzate are fermented in continuous orbatch tanks with one or more micro-organisms capable of converting fiveand six-carbon sugars into alcohol and carbon dioxide. The majority ofacetic acid, which may inhibit fermentation, was removed in the previousevaporation step. Some additional acetic acid may be formed in thefermentation steps. Nutrients and pH adjustment chemicals, as well asmake-up fermentative organism, are added in the fermentors as and ifneeded. Carbon dioxide is removed from the fermentors and scrubbed withcool water for alcohol recovery. This purified gas can be furthercompressed and sold as industrial grade carbon dioxide. The fermentationbroth, commonly termed “beer”, from the fermentation step is sent to adistillation column.

The eighth step of the process is distillation of alcohol. The beer fromthe fermentation processes is sent to a distillation column to separatethe alcohol from the solids and residual sugars. Alcohol leaving as theoverhead from the distillation column is recovered at approximately 50mass-% strength. The final concentration of the alcohol product isperformed in a rectifying column and molecular sieve to obtain over99-mass % alcohol. In one manifestation, the beer column is integratedin the existing Kraft mill multiple-effect evaporator train so that itruns as an effect and avails itself of the multiple effect economy ofthe Kraft evaporator.

The ninth step of the process is the solids concentration from thestillage. The solids, commonly termed stillage, from the distillationbeer column bottom can be further evaporated in an optional mechanicalvapor concentrator to achieve zero-liquid discharge operation. Theconcentrated sludge can be burned in a biomass boiler to increase steamgeneration. Alternatively, this concentration can happen by injectingthe distillation bottoms in the weak black liquor of the existing Kraftmill, so that it is evaporated using multiple-effect economy in theexisting Kraft evaporator.

The tenth step of the process is combustion of biomass. The compactedbiomass from the third step and concentrated solids from the ninth stepare fed to a traditional biomass combustion unit. The heat of combustionis used to raise steam, which drives a steam turbine to generateelectricity, or the steam can be used for the process.

In one manifestation of the invention, hydrolysis and fermentation (theseventh and tenth steps) may be combined in one step by using a thirdparty proprietary microorganism.

What is claimed is:
 1. A process for the production of alcohol frombiomass, said process comprising: (a) extracting a biomass feedstockwith steam or hot water, to generate a first liquid hydrolyzate and afirst extracted-solids stream; (b) extracting wood chips with steam in adigester, to generate a second liquid hydrolyzate and a secondextracted-solids stream; (c) combining said first liquid hydrolyzate andsaid second liquid hydrolyzate to generate a combined hydrolyzate; (d)further hydrolyzing said combined hydrolyzate with an acid or enzymes toconvert oligomeric hemicelluloses into monomer sugars; and (e)fermenting said monomer sugars to produce an alcohol.
 2. The process ofclaim 1, wherein said alcohol is ethanol or butanol.
 3. The process ofclaim 1, said process further comprising dewatering and combusting saidfirst extracted-solids stream to produce power.
 4. The process of claim1, said process further comprising pulping said second extracted-solidsstream to produce pulp.
 5. A process for the production of alcohol andpower from biomass, said process comprising: (a) extracting a firstbiomass feedstock with steam or hot water, to generate a first liquidhydrolyzate and a first extracted-solids stream; (b) optionallyextracting a second biomass feedstock, in the form of wood chips, withsteam in a Kraft digester, to generate a second liquid hydrolyzate and asecond extracted-solids stream; (c) further hydrolyzing said firstliquid hydrolyzate and, if step (b) is conducted, said second liquidhydrolyzate, with an acid or enzymes to convert oligomerichemicelluloses into monomer sugars; (d) fermenting said monomer sugarsto produce an alcohol; (e) combusting said first extracted-solids streamto produce power; and (f) if step (b) is conducted, pulping said secondextracted-solids stream to produce pulp.
 6. The process of claim 5, saidprocess further comprising evaporating said first liquid hydrolyzateand, if step (b) is conducted, said second liquid hydrolyzate usingmechanical-vapor recompression evaporation.
 7. The process of claim 5,wherein said first liquid hydrolyzate and, if step (b) is conducted,said second liquid hydrolyzate is each maintained at a pH below 4.8 tovolatilize acetic acid during said evaporating.
 8. The process of claim5, wherein production and purification of said alcohol is integratedwith a host Kraft pulp mill, to minimize heat loss and energy use. 9.The process of claim 5, wherein a separate multiple-effect evaporatorlocated at a host Kraft pulp mill is integrated with an alcoholdistillation column for purifying said alcohol.
 10. The process of claim5, said process further comprising injecting distillation column bottomsinto weak black liquor of a Kraft pulp mill, to concentrate saiddistillation column bottoms.
 11. The process of claim 5, said processfurther comprising combining concentrated distillation column bottomswith said first extracted-solids stream prior to said combusting. 12.The process of claim 5, wherein step (e) produces high-pressure steamsuitable for a turbine to generate said power, and wherein used steamfrom step (e) is recycled to step (b), if conducted, and/or step (c).13. A process for the production of alcohol and pulp from biomass, saidprocess comprising: (a) extracting a first biomass feedstock, in theform of wood chips, with steam in a Kraft digester, to generate a firstliquid hydrolyzate and a first extracted-solids stream; (b) optionallyextracting a second biomass feedstock with steam or hot water, togenerate a second liquid hydrolyzate and a second extracted-solidsstream; (c) further hydrolyzing said first liquid hydrolyzate and, ifstep (b) is conducted, said second liquid hydrolyzate, with an acid orenzymes to convert oligomeric hemicelluloses into monomer sugars; (d)fermenting said monomer sugars to produce an alcohol; (e) pulping saidfirst extracted-solids stream to produce pulp; and (f) if step (b) isconducted, combusting said second extracted-solids stream to producepower.
 14. The process of claim 13, said process further comprisingevaporating said first liquid hydrolyzate and, if step (b) is conducted,said second liquid hydrolyzate using mechanical-vapor recompressionevaporation.
 15. The process of claim 13, wherein said first liquidhydrolyzate and, if step (b) is conducted, said second liquidhydrolyzate is each maintained at a pH below 4.8 to volatilize aceticacid during said evaporating.
 16. The process of claim 13, whereinproduction and purification of said alcohol is integrated with a hostKraft pulp mill, to minimize heat loss and energy use.
 17. The processof claim 13, wherein a separate multiple-effect evaporator located at ahost Kraft pulp mill is integrated with an alcohol distillation columnfor purifying said alcohol.
 18. The process of claim 13, said processfurther comprising injecting distillation column bottoms into weak blackliquor of a Kraft pulp mill, to concentrate said distillation columnbottoms.
 19. The process of claim 13, wherein step (b) is conducted,said process further comprising combining concentrated distillationcolumn bottoms with said second extracted-solids stream prior to saidcombusting.
 20. The process of claim 13, wherein step (b) is conducted,wherein step (f) produces high-pressure steam suitable for a turbine togenerate said power, and wherein used steam from step (f) is recycled tostep (a) and/or step (c).